The disclosed embodiments relate generally to an alignment mechanism, and more particularly, to a mechanism that may be utilized to provide a normal force component to a device, such as a thermally controlled semiconductor device.
When testing a semiconductor device, a thermal control device may be used to regulate the temperature of the device while the device is being tested. The thermal control device may include, for example, a heat exchanger, a heating device (such as a heated plate or a Peltier device), or a cooling device. Further, device temperature may be controlled passively or actively based on feedback, such as feedback associated with present or historical device temperature or power consumption. Thermal control devices may be used to cool or heat a device, or may be used to maintain a device at a substantially constant temperature.
One type of thermal control device utilizes a heat exchanger, which may include a heat sink or active heating/cooling elements to maintain the device at a setpoint temperature during testing. The heat exchanger may be incorporated into a thermal head that applies a force to the device. The force is provided to ensure that there is proper heat transfer between the thermal head and the device during testing. While sufficient force is required to maximize thermal transfer, the contact force must also be controlled to avoid damage to the device.
In such environments, there may be external forces that cause the contact force on the device applied by a thermal head to be applied off center on the device. Such external forces may include an off-center mass of the thermal head combined with gravity (e.g., horizontal plunging of a device under test into a test socket opposite to the thermal head), and fluid conduits, such as bellows, with varying spring rates and/or free lengths. The applied force of the thermal head must be large enough to overcome these external forces. Further, it may be beneficial for heat transfer purposes if contact surfaces of the device and the thermal head are in intimate and even contact, preferably oriented parallel to each other, in order to reduce thermal resistance across contacting surfaces, which is a function of the quality of the contact (e.g., contact pressure, alignment, surface flatness, materials, etc.).
By way of example, FIG. 1 illustrates a control system for maintaining the temperature of a device, such as an integrated circuit chip 10 (IC-chip), near a setpoint (e.g., approximate real-world operating temperature, room temperature, optimal operating temperature) while the IC-chip is connected to a test socket 24. Such a system is described in U.S. Pat. No. 7,199,597, the contents of which are hereby incorporated in their entirety. The system includes an electric heater 20 and an evaporator 21 having an input conduit 21a and an output conduit 21b, which together form a heat exchanger.
Temperature of the IC-chip 10 is maintained near the setpoint using two feedback loops in the control system of FIG. 1. A first feedback loop comprises a control circuit 26, a power supply 25, and the electric heater 20. The first feedback loop compensates for changes in power dissipation in the IC-chip. The second feedback loop comprises a control circuit 27 for a valve 22 and the evaporator 21. The control circuit 27 generates a signal SFy on conductors 22b in response to signals SPH, STE, and SP, which are received on conductors 25a, 21d, and 26a, as further explained in U.S. Pat. No. 7,199,597. In order to control IC-chip temperature in such a system or in similar systems using conductive heat transfer, it is beneficial for effective heat transfer to maintain a uniformly distributed compressive force between contact surfaces of the IC-chip 10 and the heat exchanger, such as the electric heater 20.
Generally, prior art methods attempt to ensure proper heat transfer between the thermal head and the IC-chip by applying a force through a sliding interface within the heat exchanger. The sliding interface allows the contact surface of the heat exchanger to adjust laterally (i.e., to slide) to compensate for misalignment with the contact surface of the IC-chip. Such systems rely on low frictional forces within the sliding interface to allow less restricted movement in directions perpendicular (e.g., lateral, transverse) to the direction of the applied force (e.g., normal, longitudinal). As applied forces increase, however, the frictional forces within the sliding interface proportionally increase. This increase of the frictional forces between the IC-chip and the thermal head results in decreased ease of motion.
According to at least one theoretical model, if a normal load is applied between two surfaces, there is a limit as to the angle that the two surfaces may be oriented off of a plane perpendicular to the normal load, before the two surfaces slip relative to one another. The angle is a function of the coefficient of friction between the two surfaces, which may be relatively low for an IC-chip and a heat exchanger. As such, a relatively low coefficient of friction may lead to slipping of the surfaces.
One prior art assembly that utilizes a heat exchanger for thermal control of a device is described in U.S. Pat. No. 6,116,331 (“the '331 patent”). The '331 patent discloses a heat exchanger that is held spaced-apart from a frame by a leaf spring, which extends from one side of the frame to the other side of the frame. The heat exchanger contacts the leaf spring near the middle of the leaf spring. The leaf spring moves the heat exchanger so that the heat exchanger can be placed flush against a device. The '331 patent relies on the heat exchanger contact points with the leaf spring to create a low friction interface. Additionally, the leaf spring consumed a large volume of space in a lateral direction.
U.S. Pat. No. 4,791,983 discloses an assembly in which a coil spring presses a planar surface of a liquid cooling jacket against a planar surface of a device. The coil spring is compressed in a direction perpendicular to the planar surface of the liquid cooling jacket and the device to squeeze the planar surfaces together and thereby lower thermal resistance therebetween. The assembly according to the '983 patent, however, is designed for use in an operational environment, such as a server system, and is not adapted for systems in which the device is repeatedly removed from contact with the heat exchanger.
U.S. Pat. Nos. 7,243,704 and 7,373,967, the contents of which are hereby incorporated by reference in their entireties, describe systems utilizing a coil spring to exert a compressive force on the face of a heat exchanger and the surface of a device under test, such as an IC-chip. These systems are adapted for use in a test assembly in which an IC-chip is inserted into a socket of a test device, and the IC-chip is maintained near a setpoint by a heat exchanger during testing. In such systems, rotations (e.g., pivoting, misalignment) of the thermal head mating with the IC-chip may cause the applied force to be off center. If the applied force is off center, the resulting pressure distribution between the thermal head and IC-chip may not be uniform, possibly causing stress concentrations and varying temperature distributions due to varied thermal resistance (a function of contact pressure) across the contact between the heat exchanger and IC-chip. If the applied force is too far off center, the thermal head may even tilt or fall off of the device because the center of force of the thermal head will be off of the support base provided by the device.
It would be advantageous to provide an alignment mechanism that allows for improved centrality of the contact force between a first device, such as a thermal control unit or heat exchanger, and a surface of a second device, such as a semiconductor device, an IC-chip, etc., where the alignment mechanism permits lateral movement of the first device so as to accommodate angular misalignment between contact surfaces of the first and second devices.